Performance monitors that measure the kinematics of a golf club and ball, such as those described by U.S. Pat. Nos. 6,533,674 and 6,500,073, are well known in the art. The most sophisticated of these devices utilize digital imaging devices to optically acquire spatial information of the golf clubs and balls. To determine kinematics, at least two time spaced images which contain spatial information must be acquired.
Performance monitors typically use an optical system to acquire the time spaced images. The optical systems generally have a fixed field of view, and therefore a triggering system is required to activate image acquisition as the ball or club enters the field of view. This may be complicated by the fact that the club velocity may vary. For example, a pitching wedge may move at approximately 40 mph, while a driver may move at about 120 mph. Since the velocity of the ball or club may vary dramatically, the time interval between consecutive images must be controlled to ensure that at least two images are acquired within the field of view.
Typically, this has been accomplished by using a trigger sensor that determines the spatial position and velocity of the club or ball. The trigger sensor is then attached to a computational device, such as a microprocessor or an electronic gate array, to compute activation times for the imaging system.
Prior art devices have used a sensor consisting of a pair of lasers to determine position and velocity. One such laser sensor is described by U.S. Pat. No. 6,561,917. However, laser devices have several deficiencies. Primarily, they are susceptible to interference from sunlight. This can cause errors, which may lead to an incorrect dwell time. Additionally, they may also require reflectors for long range operation, may require separate emitter and receiver bodies, are expensive, and may pose a safety risk. These deficiencies make laser sensors obtrusive to the golfer, and present the operator of the performance monitor with added burden.
A continuing need exists for an accurate, inexpensive triggering system that is not susceptible to outside interference.